A case of disseminated Kaposi sarcoma in a 76-year-old woman treated with low-dose steroids for a seronegative polyarthritis is described. HIV serology was negative, whereas PCR for HHV-8 was positive. The patient presented with a profound reduction in the peripheral blood CD4+ cell count and a decrease in serum immunoglobulins and was diagnosed as having idiopathic CD4+ lymphocytopenia. The clinical picture was characterized by limited cutaneous lesions with typical features of KS associated with widespread visceral involvement and unusually aggressive behaviour.